This invention relates to a method for cholesterol removal in egg and egg yolk products to produce a cholesterol-reduced whole egg product.
Eggs are a popular and desirable component of the human diet both in terms of taste and nutritional value. The liquid portion of whole egg consists of about 64% white and 36% yolk. The egg white or egg albumen is essentially an aqueous solution of proteins containing small amounts of minerals and sugars with only a trace of fat. However, the egg yolk contains virtually all the fat and cholesterol of whole eggs. Unfortunately, egg yolk is very high in cholesterol, with a cholesterol content of approximately 1.2% of the egg yolk weight. Furthermore, about one-third of the yolk weight is fat. Fatty acid analysis shows that the fat content of an average yolk is 35.4% saturated fat (principally palmitic and stearic acids), 49.1% monounsaturated fat (oleic acid), and 15.5% polyunsaturated fat (linoleic acid). Thus, the ratio of polyunsaturated fat to saturated fat is less than 1 to 2, which is an undesirable balance.
Several approaches have been utilized to reduce cholesterol levels in food products. For example, U.S. Pat. No. 4,804,555 discloses a process for the simultaneous deodorization and cholesterol level reduction of fish oils. The fish oil is deaerated, mixed with steam, heated, flash vaporized, thin film-stripped with a countercurrent stream, and cooled. U.S. Pat. No. 4,255,455 describes a process for preparing casein with lowered cholesterol content. The process comprises dispersing a casein-cholesterol bond-reducing emulsifying agent in an aqueous medium containing casein and cholesterol, with subsequent isolation of casein from the medium.
A number of methods have been developed to remove cholesterol from egg products and egg yolks. One approach utilizes microorganisms to enzymatically oxidize and degrade cholesterol [Japanese Patent 60-18375], but this method produces cholesterol oxidation products which may be undesirable. Another enzymatic approach is described in U.S. Pat. No. 4,980,180 where .alpha.-amylase is mixed with egg yolk to facilitate the removal of .beta.-cyclodextrin. An alternative approach to cholesterol reduction is described in U.S. Pat. No. 4,882,193, where a low fat egg product is produced by diluting overly rich yolks with albumin.
Another approach to cholesterol removal is to extract cholesterol using organic solvents such as diethyl ether, methylene chloride, ethyl acetate, hexane, and benzene [JP 48/44458, U.S. Pat. Nos. 4,104,286, 3,881,034, 3,563,765, 4,234,619 and Tokarska, et al., Can. Inst. Food Sci. Tech. J., 18:256-258 (1985)]. For example, U.S. Pat. No. 2,234,619 describes a method for cholesterol removal from eggs by dehydrating the eggs, extracting the cholesterol with liquid dimethyl ether under anhydrous conditions and removing the dimethyl ether by treatment under reduced pressure at low temperatures. U.S. Pat. No. 4,104,286 describes the isolation of cholesterol from eggs through extraction with ethanol, saponification in an aqueous ethanolic alkali metal hydroxide and concentration and purification with a hydrocarbon solvent and methanol.
Solvent extraction processes have several disadvantages. First, solvent extraction and subsequent drying results in the yolk having poor taste and texture when cooked. Second, solvent extraction methods may involve significant processing steps to remove solvents. Third, even with supercritical carbon dioxide as the solvent, the selectivity of cholesterol extraction over triglycerides may be limited [Prepared Foods, 157:186 (1988); JP 59/135847].
Edible vegetable oils have also been used to extract cholesterol from egg yolks, as described in U.S. Pat. Nos. 3,717,414; 4,103,040 and 4,333,959. U.S. Pat. No. 3,594,183 describes the extraction of fat and cholesterol from egg yolk with vegetable oil, salt, emulsifiers, and coloring agents, followed by drying.
Thus, it would be desirable to provide egg products having desirable functional characteristics of egg yolk products (e.g., protein and phospholipids), while reducing the cholesterol level and increasing the polyunsaturated fat to saturated fat ratio. It would further be desirable to do this while retaining the functionality, appearance and taste of natural eggs which would yield good texture upon being cooked, thus avoiding dried egg products and the like.